It would lead to the screen becoming unlocked, iirc.
Edit: Just to add a bit more detail. xscreensaver locks the screen by putting a window across it that grabs ownership of input devices. Thus if it crashes, the window goes away and the inputs released.
Yes. But xscreensaver only use straight xlib to paint any UI elements. JWZ's argument is that this reduce the chance of bugs vs using the likes of GTK or Qt to draw password prompts etc.
Looking at bug tracker activity so far would suggest that it does, but of course, the stats might be skewed by far more people using a Gnome/Unity/Cinnamon/whatever-ified version of xscreensaver than the vanilla one.
I read about that bug a while ago. It was due to mishandling a strange X11-specific cornercase; to be fair, that's the kind of stuff that is certainly more aptly handled (in the X11 world) in a toolkit (X11-specific cornercases are like 30% of the reason why, as soon as alternatives to Xlib were available, everyone embraced them and cried tears of joy), which would suggest that not relying on toolkits opens xscreensaver's locker to other issues that are more aptly handled in a toolkit.
However, if you look over the bugs that Gnome, Cinnamon or Unity's wrappers had... I'm inclined to think that there are a lot more trivial problems (like the one I linked in my other comment, here : https://news.ycombinator.com/item?id=11412688 ) in Gnome's a thousand and one libraries than there are cornercases in X11.
Edit: Just to add a bit more detail. xscreensaver locks the screen by putting a window across it that grabs ownership of input devices. Thus if it crashes, the window goes away and the inputs released.